The present invention generally relates to a method for fabricating semiconductor devices incorporating capacitor elements formed of refractory metal-silicon-nitrogen and devices formed and more particularly, relates to a method for fabricating semiconductor devices that incorporates capacitor elements formed by depositing multi-layers of refractory metal-silicon-nitrogen in the same process chamber by varying processing conditions and devices formed by such fabrication.
In semiconductor fabrication, capacitors are frequently formed in-situ in a semiconductor structure. For instance, an in-situ formed capacitor can be found in a dynamic random access memory device. The process required for forming the capacitor is complicated. It involves the deposition of different layers of materials by different chemical processes, and most likely, in different process chambers. For instance, layers deposited of a polysilicon material are frequently used as the electrode, while layers deposited of an insulating material such as silicon oxide are frequently used as the capacitor dielectric. The process therefore requires multiple number of depositions, from multiple number of different materials conducted in multiple number of process chambers for the forming and patterning of the capacitor.
In modern semiconductor devices, refractory metals have been frequently used in semiconductor processes to form vias or contacts. However, refractory metal-nitrogen alloys have not been used widely in the processing of semiconductor devices. For instance, only recently, U.S. Pat. No. 5,892,281 describes the use of tantalum-aluminum-nitrogen alloys in semiconductor devices as a diffusion barrier and an adhesion promoter. The patent discloses the use of Taxe2x80x94Alxe2x80x94N in a semiconductor device to prevent inter-diffusion between surrounding layers, for instance, between two conductor layers; between a semiconductor layer and a conductor layer; between an insulator layer and a conductor layer; between an insulator layer and a semiconductor layer; or between two semiconductor layers. A second use of Taxe2x80x94Alxe2x80x94N is to promote adhesion with adjacent layers, for instance, between two conductor layers; between a conductor layer and an insulator layer; between a semiconductor layer and a conductor layer; or between two semiconductor layers. However, U.S. Pat. No. 5,892,281 does not teach any other uses for tantalum-aluminum-nitrogen alloys in conductor fabrication.
It is therefore an object of the present invention to provide a method for forming a capacitor in-situ in a semiconductor structure that does not have the drawbacks or the shortcomings of the conventional methods.
It is another object of the present invention to provide a method for forming a capacitor in-situ in a semiconductor structure that requires only the deposition of a single material.
It is a further object of the present invention to provide a method for forming a capacitor in-situ in a semiconductor structure that requires only the deposition of a single material of refractory metal-silicon-nitrogen in multiple layers.
It is another further object of the present invention to provide a method for forming a capacitor in a semiconductor structure that requires only the deposition of a single material of TaSiN in multiple layers under different processing conditions.
It is still another object of the present invention to provide a method for forming a capacitor in a semiconductor structure by depositing multiple layers of a refractory metal-silicon-nitrogen each having a different stoichiometry.
It is yet another object of the present invention to provide a method for forming a capacitor in-situ in a semiconductor structure by depositing multiple layers of a refractory metal-silicon-nitrogen each having a different sheet resistance value.
It is still another further object of the present invention to provide a method for forming a capacitor in a semiconductor structure by depositing multiple layers of refractory metal-silicon-nitrogen in the same chamber by varying a flow rate of partial pressure of nitrogen into the chamber.
It is yet another further object of the present invention to provide a semiconductor capacitor structure which has a lower electrode, a middle dielectric layer and an upper electrode formed of the same refractory metal-silicon-nitrogen material but with different stoichiometry.
In accordance with the present invention, a method for forming a refractory metal-silicon-nitrogen capacitor in a semiconductor structure and the structure formed are disclosed.
In a preferred embodiment, a method for forming a refractory metal-silicon-nitrogen capacitor in a semiconductor structure can be carried out by the operating steps of positioning a preprocessed semiconductor substrate in a sputtering chamber; flowing Ar gas into the sputtering chamber; sputter depositing a first refractory metal-silicon-nitrogen layer on the substrate from a refractory metal silicide target, or from targets of a refractory metal and a silicon; flowing N2 gas into the sputtering chamber such that concentration of the N2 gas in the chamber is at least 35% by adjusting the flow rate or partial pressure of N2; sputter depositing a second refractory metal-silicon-nitrogen layer on top of the first refractory metal-silicon nitrogen layer; stopping the N2 gas flow into the sputtering chamber; sputter depositing a third refractory metal-silicon-nitrogen layer on top of the second refractory metal-silicon-nitrogen layer; and photolithographically forming the first, second and third refractory metal-silicon-nitrogen layers into a capacitor.
The method for forming a refractory metal-silicon-nitrogen capacitor in a semiconductor structure may further include the step of in-situ annealing the capacitor at a temperature of at least 80xc2x0 C., or the step of flowing Ar gas into the sputtering chamber at a flow rate between about 10 sccm and about 200 sccm, or the step of flowing N2 gas into the sputtering chamber at a flow rate between about 1 sccm and about 100 sccm. The method may further include the step of sputter depositing the first and the third refractory metal-silicon-nitrogen layer to a thickness between about 100 xc3x85 and about 5000 xc3x85, or the step of depositing the second refractory metal-silicon-nitrogen layer to a thickness between about 100 xc3x85 and about 5000 xc3x85. The method may further include the step of sputter depositing the first and the third refractory metal-silicon-nitrogen layer each having a sheet resistance of not higher than 50 ohm/sq., or the step of sputter depositing the second refractory metal-silicon-nitrogen layer which has a dielectric constant greater than 7.5. The method may further include the step of sputter depositing the first, second and third refractory metal-silicon-nitrogen layer formed of a refractory metal selected from the group consisting of Ta, Nb, V, W and Ti.
The present invention is further directed to a semiconductor capacitor structure which includes a lower electrode formed of a first refractory metal-silicon-nitrogen material that has a sheet resistance not higher than 50 ohm/sq; a middle dielectric layer formed of a second refractory metal-silicon-nitrogen material that has a dielectric constant greater than 7.5; and an upper electrode formed of the first refractory metal-silicon-nitrogen material.
In the semiconductor structure of a capacitor, each of the lower electrode and upper electrode is formed to a thickness between about 100 xc3x85 and about 5000 xc3x85, the middle dielectric layer is formed to a thickness between about 100 xc3x85 and about 5000 xc3x85. The refractory metal in the first, second and third refractory metal-silicon-nitrogen material is selected from the group consisting of Ta, Nb, V, W and Ti. The first refractory metal-silicon-nitrogen material has a sheet resistance of not higher than 50 ohm/sq., while the second refractory metal-silicon-nitrogen material has a dielectric constant greater than 7.5.